1. Field of the Invention
The present invention relates to a method for bending Si material that can produce a high-accuracy bend in a single crystal or polycrystal silicon (hereinafter, referred simply to as xe2x80x9cSi materialxe2x80x9d) without contamination of the Si material. The present invention also relates to a core wire member made of Si material for manufacturing a polycrystal Si.
2. Description of the Related Art
In recent years, silicon (Si) has shown a remarkable growth in demand for a semiconductor material. The physical and electrical characteristics of this material as a semiconductor are noticed. In particular, Si used as a bulk material has been frequently used as a substrate for a DRAM (Direct Random Access Memory) and for an MPU (Micro Processor Unit). In addition, Si material is in great demand for wafers. Recently, wafers are being made in larger diameters. This requires that the Si ingots, from which the wafers are sliced, also has grown proportionately. Si ingots now weigh 200 kg or more. The large size and great weight are producing problems in holding and carrying the Si ingot. More specifically, in order to prevent metal contamination of the Si ingot, Si and other materials are frequently used in handling jigs and other manufacturing tools. However, as the weight and diameter of the Si ingot increase, the difficulty in manufacturing such jigs increases.
One approach to solving this problem is machining the Si ingot itself to make it easier to attach jigs for carrying. However, the brittleness of Si material makes it difficult to machine, and also, post-process washing or the like is required. For this reason, according to the aforesaid course, new problems arise such as higher cost and complication of the manufacturing process.
Moreover, in order to produce functioning semiconductors such as, for example, integrated circuits on a silicon wafer, heat treatment at high temperature and film forming are carried out in batch processing. Conventionally, a wafer holding jig used in this case is mainly quartz. Quartz is not ideal since it has different thermal characteristics from the Si material of the wafer, especially at large diameter. For this reason, a single crystal silicon board has been often used for the holding jig because single crystal silicon has the same characteristic as the wafer. Therefore, single crystal silicon is effective in decreasing contamination of the wafer. However, such a board is manufactured by cutting it from a single crystal silicon ingot. This makes such boards expensive in view of the poor mechanical workability of the material. Thus, there is a need for a method for freely bending these components so as to reduce or eliminate the need for machining.
Si is a very brittle material. For this reason, Si is fractured (destroyed) by impact when a great force is applied thereto at ordinary (room) temperature. Moreover, Si material has high strength at high temperature. For these reasons, it has been considered impossible to carry out plastic forming of Si material. In the case of compressive deformation restraining slip deformation, Si is not deformed until just as it reaches its melting point. At its melting point the material is in a transition state between rigidity and being melted. For this reason, it has been considered impossible to bend Si material.
It is an object of the present invention to provide a bending method for Si material which overcomes the drawbacks of the prior art.
The inventors have achieved the present invention on the basis of the fact that, when a bending moment is applied to a heated portion of Si material heated to a brittle-ductile transition temperature or above, slip deformation is generated. Such slip deformation makes it possible to bend the Si material without contaminating the Si material.
Briefly stated, the present invention provides a method for bending Si material, which have been considered to be very brittle, and hard to bend. The Si material is heated to at least its brittle-ductile transition temperature. A bending moment is applied to a heated portion of the Si material so that a slip deformation is generated. Whereby it is possible to perform bending, and to greatly improve a degree of freedom from machining the Si material. The Si material has a brittle-ductile transition temperature which transfers from a brittle to a ductile state at its brittle-ductile transition temperature. At the transition temperature or more, the Si material is in a state that a slip can to be generated between its crystals in response to a bending torque applied thereto. Thus, when a bending moment is applied to the heated portion of the Si material which is heated to the transition temperature or more, a slip is generated between lattices or between crystal grains in the heated portion, so that the Si material is deformed.
According to an embodiment of the invention, there is provided a bending method for Si material, comprising the following steps of: heating an Si material to at least a brittle-ductile transition temperature to produce a heated portion, and applying a bending moment to said heated portion to produce a slip deformation in said Si material.
According to a feature of the invention, there is provided apparatus for bending a Si material comprising: a rotatable arm, said rotatable arm being rotatable about an axis, a holding portion effective for clamping said Si material, means for applying a thrust to said Si material toward said rotatable arm, whereby said Si material is urged toward said rotatable arm, and said rotatable arm applies a bending moment to said Si material, means for heating said Si material upstream of said holding portion, and said means for applying a thrust including a fluid cylinder having a substantially constant flow rate of fluid fed thereto.
According to a further feature of the invention, there is provided a core wire member made of Si material comprising: first and second core wire portions extending substantially parallel with each other, a connective portion, a first junction connecting a first end of said first core wire portion to a first end of said connective portion, a second junction connecting a first end of said second core wire portion to a second end of said connective portion, and said first and second junctions being formed by bending.
According to a still further feature of the invention, there is provided apparatus for bending an Si material comprising: first means for applying a bending torque to said Si material, second means for applying a longitudinal force to said Si material toward said first means, means for locally heating said Si material between said first and second means, said second means being responsive to a reduction in temperature of said Si material to slow down an advance of said Si material, and responsive to an increase in temperature of said Si material, whereby negative feedback stabilizes bending of said Si material.
More specifically, according to the present invention, the Si material, which have been considered to be very brittle and hard to bend, is heated to a brittle-ductile transition temperature or above, a bending moment is applied to a heated portion of the Si material to generate a slip deformation. This technique permits bending Si material. Thus, it is possible to manufacture a member made of Si material, which has been conventionally manufactured only by machining. Further, it is possible to manufacture a member having a shape which is hard to be manufactured by machining, and thus, the need for machining the Si material is reduced or eliminated.
Referring to FIG. 10, a core wire member made of Si material is treated to deposit a polycrystal Si on its surface. Core wire members are arranged in a bell jar into which a silicon-bearing gas such as monosilane or trichlorosilane is introduced. Polycrystal silicon is grown on a surface of the core wire member while it is heated. This technique has the following draw backs. Conventionally, in a core wire member made of Si material for manufacturing a polycrystal Si, the following connection structure has been employed. More specifically, in each junction 33 extending from the core wire portion 31 to the connective portion 32, a rod-like core wire portion 31 and a rod-like connective portion 32, which are arranged perpendicular to each other, are mechanically connected by concavity convexity fitting or the like. In the conventional connection structure, while energizing and heating the core wire member so that the polycrystal silicon is grown on its surface, an abnormal growth of the polycrystal Si occurs at the junction 33 resulting from the following reasons. First of all, contact resistance is high in the junction 33 thereby elevating the temperature of the junction. As a result, this causes a localized abnormal growth of the polycrystal Si. Secondly, at areas where inner side portion of two rod-like members 31, 32 cross perpendicular to each other, the radiant heat from each mutually interacts with the radiant heat from the other. This elevates the temperature of the inner side portions. As a result, abnormal growth of polycrystal Si occurs in these areas.
Referring now to FIG. 11, as described above, when abnormal growth of the polycrystal Si happens in the junction 33, in the case of divisively removing the rod-like polycrystal Si, there are the following disadvantages. More specifically, in the vicinity of the junction 33 the rod-like polycrystal Si does not clearly crack in a direction perpendicular to an axial direction thereto, but instead, cracks in a slanting direction. As a result, the manufacturing yield of rod-like polycrystal Si is reduced.
Therefore, in the present invention, when bending the core wire member for growing the polycrystal Si, abnormal growth of the polycrystal Si is reduced, so that bending and cracking the rod-like polycrystal Si is readily carried out. As a result, the manufacturing yield of the rod-like polycrystal Si is improved.
To achieve the above object, the present invention provides a bending method for Si material, comprising the steps of: heating an Si material 1 having brittleness at room temperature to a brittle-ductile transition temperature or higher; and applying a bending moment to the heated portion of the Si material so that slip deformation is generated in the Si material 1.
Referring now to FIG. 1, a graph shows a relationship between the heating temperature in Si material and a plastic strain generated at break under the heating temperature. The Si-material has almost no plastic strain until the heating temperature reaches the vicinity of 700xc2x0 C. However, when the heating temperature exceeds 700xc2x0 C., plastic strain resulting from slip is gradually generated in the Si material. Then, at a temperature of 800xc2x0 C. or more, the plastic strain suddenly increases. More specifically, the Si material has a brittle-ductile transition temperature which transfers from a brittle state to a ductile state. At the aforesaid brittle-ductile transition temperature or more, the Si material is in a state permitting crystal slip to occur. Thus, when a bending moment is applied to the heated portion heated to the aforesaid brittle-ductile transition temperature or more, slip is generated between atoms or between crystal grains in the heated portion. As a result, the Si material is deformed. In this case, a heating source is not specially limited, and may use a gas, high frequency and radiant heat using high frequency or the like.
As is evident from the above description, it is possible to manufacture a member made of Si material, which has been conventionally manufactured only by machining, and further, it is possible to manufacture a member having a shape which is hard to manufacture by machining. Thus, a degree of freedom for machining the Si material is greatly improved.
Further, the present invention provides a bending method for Si material wherein a rotatable arm 5, supported for rotation around a specified shaft 5a, is provided with a holding portion 5b. A feeder mechanism 3 for feeding a rod-like Si material 1 is arranged so that the rod-like Si material 1 runs along a circular-arc orbit of the holding portion 5b. With the rod-like Si material 1 held by the holding portion 5b, a bending moment is applied to the fed rod-like Si material 1 by longitudinal feeding of the rod-like Si material 1 and by rotation of the rotatable arm 5.
According to the bending method for Si material, a rod-like Si material 1 is fed by a feeder mechanism 3 while being held by a holding portion 5b. A bending moment is continuously applied to the Si material 1 by longitudinal feed of the feeder mechanism 3 and by rotation of the rotatable arm 5. The Si material 1 is locally heated in this condition to a temperature where it exhibits plasticity. Slip deformation is generated in the heated portion to which a bending moment is applied. As a result, a bend is generated in the Si material. Thus, it is possible to carry out so-called continuous dieless bending without the use of molding dies, and to bend the rod-like Si material 1 into a smoothly circular-arc shape. Since no molding dies are used, the heated portion of the Si material does not contact the surface of molding dies. This permits carrying out bending while reducing contamination such as metal pollution and oxidation. In order to feed the Si material 1, a thrust force (propulsion) may be applied to the Si material 1 from the feeder mechanism 3 or a pressure cylinder of a driving system 2, or a traction force may be applied to the Si material 1 from the rotatable arm 5.
Further, the present invention provides a bending method for Si material, wherein rod-like Si material 1 is locally heated just downstream of the feeding location, and thereby, a heated region of the rod-like Si material 1 is successively moved along the rod-like Si material 1.
According to the bending method for Si material, a gentle temperature distribution is given to the Si material 1. Therefore, by carrying out the aforesaid continuous dieless bending, the Si material 1 is deformed while absorbing heat. Then, the deformed portion is gradually enlarged, and thus, a predetermined bending portion is realized. Whereby preferable bending is performed.
The present invention provides a bending method for Si material wherein; a rotatable arm 5 is supported for rotation around a shaft 5a. The rotatable arm includes a holding portion 5b. A fluid pressure cylinder 2 for feeding a rod-like Si material 1 while applying a thrust force (propulsion) to the Si material 1 is arranged so that its feeding direction runs tangent to a circular-arc orbit of the holding portion 5b. While the rod-like Si material 1 is held by the holding portion 5b, a bending moment is applied to the fed rod-like Si material 1 by a feed of the rod-like Si material 1 and by a rotation of the rotatable arm 5. The flow rate of fluid fed to the pressure cylinder 2 is maintained approximately constant. Heating is performed locally at a location where the rod-like Si material 1 thus fed runs on a circular-arc orbit of the holding portion 5b, or in a neighborhood position.
According to the bending method for Si of materials, since a thrust force (propulsion) of a pressure cylinder 2 is maintained by controlling the fluid flow rate to its pressure cylinder to be approximately constant, bending deformation is generated in a state that a temperature change of the heated portion of the Si material 1 and a feed speed of the Si material 1 are well-matched. That is, bending proceeds under an operating condition of, so to speak, a self-regulation operation as described below:
1) a temperature change causes a deformation resistance change;
2) the deformation resistance change brings about a bending deformation quantity change;
3) the change in the bending deformation quantity changes the feed speed;
4) the change in the feed speed again produces a temperature change.
The self-regulation in the foregoing produces stable bending.
Further, the present invention provides a bending method for Si material wherein the holding portion 5b of the rotatable arm 5 is made of the same material as the rod-like Si material 1 or of a material having a hardness greater than that of the rod-like Si material 1.
According to the bending method for Si material, bending can be carried out while limiting contamination such as metal pollution and oxidation.
If the heating temperature of the aforesaid Si material 1 is set 900xc2x0 C. or more, preferable bending is achieved. In view of limiting contamination, it is preferable that the heating temperature of the Si material 1 is set to 1300xc2x0 C. or below.
A core wire member made of Si material, which is arranged in a bell jar into which a silicon-bearing gas such as monosilane and trichlorosilane is introduced, and is used so that polycrystal silicon is grown on a surface of the core wire member when being heated, comprising: a pair of core wire portions 21, 21 extending substantially parallel with each other; and a connective portion 22 connecting one end side of the core wire portions 21, 21 to each other, each junction 23 extending from the core wire portion 21 to the connective portion 22 being formed by being subjected to bending.
The core wire member made of Si material is bent by the following steps of: heating a Si material 1 having a brittleness at a room temperature to a brittle-ductile transition temperature or more; and applying a bending moment to a heated portion of the Si material 1 so that a slip deformation is generated in the Si material 1.
On the contrary, in the core wire member for growing the polycrystal Si, each junction 23 extending from the core wire portion 21 to the connective portion 22 is formed by being subjecting to bending. Thus, in the junction 23, the aforesaid abnormal growth of the polycrystal Si is reduced, so that the work of bending and cracking the rod-like polycrystal Si is readily carried out. As a result, it is possible to improve the manufacturing yield of the rod-like polycrystal Si.